Governors are generally used to regulate the speed of internal combustion engines. Some prior art governors include electronic governors, mechanical governors having centrifugally-responsive flyweights, or air vane governors. A governor maintains an engine at a relatively stable speed. The governor generally receives an input indicative of engine speed, and actuates an engine throttle accordingly to adjust the engine speed to a desired speed. If the engine speed is too low, the governor may adjust the throttle to increase engine speed. If the engine speed is too high, the governor may adjust the throttle to decrease engine speed.
FIG. 1 illustrates a prior art governor 310 including flyweights 314 having flanges 318 that move a plunger 322. The plunger 322 engages a governor lever 326, which is interconnected to a governor arm 330. The governor 310 may also include a governor shaft that connects the governor lever 326 to the governor arm 330. A throttle link 334 is connected to the governor arm 330 and an engine throttle 338. A governor spring 342 applies a biasing force on the governor arm 330. The flyweights 314 cause the governor lever 326 to move in response to engine speed, thereby causing the throttle 338 to be adjusted to control engine speed.
Conditions associated with governors include speed droop and hunting. The engine speed generally drops when a load is applied to the engine, and this drop in engine speed is called “speed droop.” The amount of speed droop is a characteristic of a particular engine, and is in part determined by spring rate and the tension applied to the governor spring 342.
Hunting, or searching, generally occurs when a governor changes the engine speed. The governor may overshoot the desired engine speed, and the governor then oscillates back and forth about the desired speed until the governor settles on the desired speed. Hunting or searching is the movement back and forth as the governor locates the desired speed. Hunting is also in part determined by spring rate and the tension applied to the governor spring.
The governor 310 generally moves the governor arm 330 in response to engine speed. Initially, the engine generally runs at a desired no-load engine speed partly determined by the initial tension of the governor spring 342. After a load is applied on the engine, the engine speed generally decreases below the desired no-load speed, and the governor 310 adjusts the throttle 338 in an attempt to increase the engine speed to the desired speed. Similarly, after a load is removed, the engine speed increases above the desired no-load speed, and the governor 310 adjusts the throttle 338 in an attempt to decrease the engine speed back down to the desired speed. In the illustrated embodiment, the governor 310 adjusts the throttle 338 by pivoting the governor arm 330, which actuates the throttle link 334. The governor spring 342 applies a biasing force on the governor arm 330 and the throttle link 334.
The selection of the spring rate of the governor spring 342 affects the performance of the governor 310. Droop and hunting are generally functions of the spring rate of the governor spring 342. The governor spring 342 applies a biasing force on the governor arm 330. Permanent speed droop may be reduced by lowering the spring rate of the governor spring 342 to reduce the force the governor spring 342 applies on the governor arm 330. A lower spring rate provides a “looser” feel for the governor 310 and permits the governor 310 to quickly react to speed changes since there is less resistance. However, lowering the spring rate of the governor spring 342 too much generally produces other engine speed concerns, such as hunting or searching. Since the spring rate is lower, the governor spring 342 provides less of a stabilizing force, and the governor 310 may fluctuate about the desired speed. The variation in engine speed caused by hunting causes a surging of the engine. The surging is audible and creates additional noise from the engine. Due to noise restrictions and other factors, additional noise from the engine is generally undesirable.
Hunting may be reduced by increasing the spring rate of the governor spring 342 to increase the force the governor spring 342 applies on the governor arm 330. Increasing the spring rate of the governor spring 342 provides a “tighter” feel for the governor 310 and may help reduce hunting or searching because there is less freedom of movement of the governor arm 330. However, increasing the spring rate of the governor spring 342 also increases permanent speed droop after a load is applied. Since the spring 342 has a higher spring rate, the governor spring 342 provides more stabilizing force to maintain a steady speed and reduce hunting. However, the additional resistive force of the spring 342 may prevent the governor 310 from actually achieving the desired speed, which results in permanent droop.
Due to permanent droop, the desired no-load engine speed often must be increased to compensate for the permanent droop. This is accomplished by increasing the initial tension of the governor spring 342. For example, if the desired no-load speed for an engine is 3,000 rpm, the permanent droop of the governor may only permit the engine speed to return to 2,800 rpm while a load is applied. Therefore, the engine experiences a permanent speed droop of approximately 200 rpm. The no-load speed may then be increased to 3,200 rpm to permit the engine to achieve the desired engine speed of 3,000 rpm under load, due to the permanent speed droop. Increasing the no-load engine speed also increases the noise generated by the engine. As mentioned above, additional noise from the engine is generally undesirable.
In FIG. 2, the graph illustrates test data of the engine speed over time in response to various loads placed on an engine having a prior art governor 310 (FIG. 1). In the test, the load (measured in Watts “W”) on the engine was from a generator. The engine was subjected to alternating periods of no load, and incrementally increasing loads. The alternating periods of no load and loads were each approximately 40 seconds in duration. In FIG. 2, the no-load speed is set at approximately 3800 rpm. Segments 350, 358, 366, 374, 382, and 390 illustrate the engine with no load (represented by “N.L.”) at approximately 3800 rpm. Segments 354, 362, 370, 378, and 386 show the engine with incrementally increasing loads, in which the engine speed decreases from the previous no load condition.
Each decrease in engine speed during the application of a load is a speed droop, and the speed droop increases with increasing loads. In the graph, as the 2050 W load is applied between segments 382 and 386, the engine speed initially decreases, or undershoots, to about 3200 rpm before increasing back to about 3600 rpm. The approximately 200 rpm difference between 3800 rpm and 3600 rpm represents the permanent speed droop, since it remains the entire time the load is applied.
Generally, a governor spring 342, as shown in FIG. 1, having a lower spring rate provides a faster response and more accuracy, but may provide less stability. The governor 310 will quickly get in the general range of the desired engine speed, providing accuracy, but the speed will fluctuate within that range, resulting in less stability. A governor spring 342 having a higher spring rate generally provides more stability, but may have slower response, and less accuracy. The governor 310 will enable the engine to reach a certain engine speed, and will maintain that speed, providing stability. However, that certain engine speed may not be the desired speed, and is normally lower than the desired speed, resulting in less accuracy.